CPMG NMR Echo Correction for Downhole Measurement Accuracy
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Solution Overview
Problem
Existing NMR measurements in downhole environments suffer from noise and artifacts, leading to reduced accuracy when attempting to quickly acquire data, which affects the reliability of hydrocarbon exploration and production decisions.
Innovation Solution
Implementing a method that includes performing modified Carr-Purcell-Meiboom-Gill (CPMG) measurements with phase-shifted excitation and refocusing pulses to generate transient-corrected echo trains, which corrects for echo amplitude variations and removes out-of-phase components, thereby improving the accuracy of NMR measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If NMR measurements are acquired quickly, then productivity is improved, but measurement precision deteriorates due to noise and artifacts
Solution Approach 1:
The patent applies preliminary action by performing a modified CPMG measurement with specific phase shifts before the main measurement sequence. The first refocusing pulse is shifted by 0 or π radians relative to the excitation pulse, and the second refocusing pulse is shifted by π/2 or -π/2 radians, preparing the spin system in advance to eliminate transient effects and out-of-phase components in subsequent measurements
Solution Approach 2:
The patent changes the phase parameters of the refocusing pulses in the CPMG sequence. Specifically, the first refocusing pulse phase is set to 0 or π radians relative to the excitation pulse, and the second refocusing pulse phase is set to π/2 or -π/2 radians, which transforms the measurement sequence to correct for transient effects and improve signal accuracy
2Device complexity
If conventional CPMG measurement is used, then device complexity is kept simple, but measurement precision deteriorates due to echo transient effects
Solution Approach 1:
The modified CPMG sequence performs a preliminary measurement with specific phase shifts to characterize and correct for transient effects. This preliminary action captures the transient behavior and enables correction factors to be applied to subsequent measurements, improving echo amplitude accuracy without significantly increasing overall system complexity
Solution Approach 2:
The patent implements feedback by using the results from the modified CPMG measurement to determine correction factors that are then applied to the main CPMG measurement sequence. The feedback loop continuously refines the measurement accuracy by adjusting for transient effects based on observed signal characteristics
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method enhances the accuracy of NMR measurements, allowing for more precise identification and quantification of fluids in porous formations, thereby improving the efficiency of oil and gas operations.
Implementation Method 1
nuclear magnetic resonance (NMR) to measure the response of nuclear spins in formation fluids to applied magnetic fields
Data Source
AI summary
The method includes performing, using a nuclear magnetic resonance (NMR) tool, a Carr-Purcell-Meiboom-Gill (CPMG) measurement by transmitting a first excitation pulse and a first plurality of refocusing pulses, and obtaining a first set of NMR echo signals. The method also includes performing a modified CPMG measurement by transmitting a second excitation pulse and a second plurality of refocusing pulses, and obtaining a second set of NMR echo signals. The second excitation pulse is shifted by 0 or π radians relative to the first excitation pulse. A first refocusing pulse of the second plurality of refocusing pulses is shifted by 0 or π radians relative to the second excitation pulse. A subsequent refocusing pulses are shifted by π/2 or −π/2 radians relative to the second excitation pulse. Further, the method includes obtaining a transient-corrected echo train based on the CPMG measurement and the modified CPMG measurement.